The invention relates to means for automatically focusing a television camera, and particularly to a circuit for obtaining data during the setup procedure which accurately defines the optimum focus conditions.
Various schemes are available in the television camera art, to provide for the manual and/or automatic focus of electronic news gathering (ENG) or of broadcast quality studio cameras.
Thus for example, typical prior art focusing systems employ a conventional resolution chart having vertically extending lines of varying spacings to define grids across which the beam is scanned. The line grids may be replaced, in other systems, with spaced series of wedgeshaped lines of selected spacings. The various types of grids are generally placed in the center of the chart, i.e., in automatic setup camera systems, in the center of a diascope test pattern where the focus conditions are at an optimum. As the beam is scanned across the various grids during the camera setup mode, an alternating waveform is generated by the tube and is detected. Optimum electrical focus conditions exist when the peak-to-peak values of the waveform are at a maximum. The maximum detected values are used during the camera operating mode by manually setting potentiometer means, or by automatically applying an electrical focus correction via an automatic error corrector system.
Prior art automatic focusing systems thus utilize analog means for measuring and correcting the focus of cameras, and therefore have the disadvantages inherent in analog systems, i.e., drift, noise, etc. In addition, prior systems require the use of an additional chart, i.e., the resolution chart with grids of previous mention.